A metal automobile frame of extruded members comprises a number of extruded, constant-section, linear bars welded to one another at structural nodes defined by connecting bodies with pockets for housing the ends of the linear bars.
The linear bars are hollow, and normally have a closed polygonal cross section. At certain points on the frame, openings must be formed through one or more linear bars to house component parts of the automobile, as, for example, at the attachments for the front or rear suspensions.
Forming an opening in one wall of a linear bar, however, locally reduces the mechanical strength of the bar, which must be compensated by increasing the thickness, and therefore greatly increasing the weight, of the bar.